This invention is directed to the construction of a secondary, lithium battery.
Lithium ion or secondary lithium batteriers are known. See: Linden, D., Ed., Handbook of Batteries 2nd Edition, McGraw Hill Inc., New York, N.Y. (1995), Chapter 36; and Besenhard, J. O. Ed., Handbook of Battery Material, Wiley-VCH Verlag GmbH, New York, N.Y. (1999). These batteries are the state of the art power sources for portable electronic devices, such as: laptop computers, cellular phones, and the like. While these batteries have enjoyed an excellent safety record, efforts to improve their safety continues.
The safety concern arises from the threat of, for example, cell rupture arising from a thermal runaway situation. The cell""s components, electrolyte and lithium containing electrodes, are packaged in a sealed metal can. In thermal runaway, heat is generated within the cell that could raise the temperature of the electrolyte and lithium electrodes above their ignition temperature. See: Hatchard, T. D. et al, xe2x80x9cImportance of Heat Transfer by Radiation in Li-ion Batteries during Thermal Abuse,xe2x80x9d Electrochemical and Solid State Letters, vol. 3, no. 7, pages 305-308 (2000), incorporated herein by reference.
Thermal runaway may arise from several different situations, but those of concern here arise from xe2x80x9cabusexe2x80x9d (or xe2x80x9cthermal abusexe2x80x9d). Abuse is qualified by several standard tests including the xe2x80x9cnail penetrationxe2x80x9d test, the xe2x80x9ccrushxe2x80x9d test, and the xe2x80x9cshort circuitxe2x80x9d test. See, for example, UL1642xe2x80x94Standard for Lithium Batteries (Underwriters Laboratories Inc., 1st Edition 10/1985 and 2nd Edition 11/1992); and xe2x80x9cGuideline for Safety Evaluation on Secondary Lithium Cells,xe2x80x9d Japan Storage Battery Association, Tokyo, Japan (1995), both are incorporated herein by reference. In the first two mentioned tests, the cell is physically damaged thereby bringing about contact of the anode and cathode (a short circuit) which leads to thermal runaway. In the latter test, the anode and cathode are externally electrically coupled (a short circuit) which leads to thermal runaway.
In the short circuited battery, a localized heat spot begins forming within the cell. This heat accelerates the chemical reactions (between anode and cathode via electrolyte) going on within the cell which creates an escalating heat producing situation (the heat production is also rapid, e.g. seconds) that should be avoided because of the potential adverse consequences. The potential adverse consequences and the importance of heat transfer out of a cell is known. See: Hatchard, Ibid. In Hatchard, a label on the exterior of the package (can) is used to improve the heat transfer from the can. The label is used to regulate the internal temperature of the can.
In a conventional secondary lithium cell (either cylindrical or prismatic), the microporous separator membrane between the anode and cathode is wrapped several times around the exterior of the wound anode, cathode, separator, prior to its insertion into the package (can). These additional wraps of the separator act as an insulator (thermal and electrical). The electrode comprises an electrode active mix and a current collector. The current collector for the negative electrode (anode) is a copper foil. The current collector for the positive electrode (cathode) is an aluminum foil. The cans are made of iron-based materials (e.g. steel) or aluminum. In a conventional cylindrical cell, for example, an 18650 (18 mm diameter and 65 mm long), the electrode closest to the interior surface of the can is the negative electrode (anode), having a copper foil current collector, the can body which is made of the iron-based material is the negative terminal of the battery, while the lid of the can is the positive terminal. In the conventional prismatic cell, two constructions are recognized. First, the negative electrode (i.e. copper current collector) is closest to the interior surface of the can (i.e. iron-based). Second, the positive electrode (i.e. aluminum current collector) is closest to the interior surface of the can (i.e. aluminum).
The instant invention is directed to a secondary lithium battery. The battery includes a negative electrode, a positive electrode, a separator sandwiched between the electrodes, an electrolyte impregnating the separator and being in a fluid communication with the electrodes, and a metal package adapted for containing the electrodes, the separator, and the electrolyte. One of the electrodes is in thermal contact with the package.